1. Field of the Invention
The present invention relates to a program control system for a magnetic recording media, and more particularly to a magnetic type digital-analogic position-sensing device.
2. Description of the Prior Art
The existing sensing devices for measuring a displacement of a rotary or linear displacement device for a motor or a linear motor can be divided into two types: magnetic type and optical type. The optical type sensing devices are better than the magnetic type sensing devices in precision, so the industries which seek high precision will adopt the optical type sensing devices. A conventional optical sensing device, as shown in FIG. 1, consists of an optical scale A and a sensor B. The optical scale A includes four parallel-arranged elongated scale elements A1, A2, A3, A4, and each of the scale elements A1, A2, A3, A4 includes plural through holes A11, A21, A31, A41. The length of the through holes A11, A21, A31, A41 of the respective scale elements A1, A2, A3, A4 is the same and identical to the distance between each pair of neighboring through holes A11, A21, A31, A41 of the respective scale elements A1, A2, A3, A4. Further as shown in FIG. 2, the length of the through holes A11 of the first scale element A1 is two times as long as that of the through holes A21 of the second scale element A2, the length of the through holes A21 of the second scale element A2 is two times as long as that of the through holes A31 of the third scale element A3, and the length of the through holes A31 of the third scale element A3 is two times as long as that of the through holes A41 of the fourth scale element A4. The sensor B is provided with four digital sensing readers B1, B2, B3, B4 opposite the respective four scale elements A1, A2, A3, A4. The respective sensing readers B1, B2, B3, B4 will output a high or low signal depending on if there are the through holes of the respective scale elements A1, A2, A3, A4 or not. The signals outputted from the four sensing readers B1, B2, B3, B4 are integrated as shown in FIG. 3, so that the relative distance between the sensing device B and the optical scale A can be known from the signals of that time.
Since the length of the through holes A11, A21, A31, A41 of the respective scale elements A1, A2, A3, A4 and the distance between each pair of neighboring through holes A11, A21, A41 of the respective scale elements A1, A2, A3, A4 determine the resolution of the sensing device B (the resolution is the minimum value to measure the displacement of the sensor B). The length of through holes A11, A21, A31, A41 and the distance between each pair of neighboring through holes A11, A21, A31, A41 of the respective scale elements A1, A2, A3, A4 of the optical scale A in the optical type sensing device can be finely formed by adopting the nano technology, so that the precision is relatively high. On the contrary, the magnetic sensing device uses the magnetic scale in which N poles and S poles are alternately arranged to make the sensing reader to output a high or low signal. Since the distance between the N pole and S pole of the magnetic type sensing device cannot achieve the normal precision of the optical type sensing device, the high precision industries will select the optical type sensing devices.
However, the more precise the optical type sensing device is, the better the working environment is needed (if the working environment is not good enough, the dust or particles are likely to obstruct the through holes of the scale elements to greatly lower the precision). Since the general industries cannot provide the location with better working environment satisfying the requirements of the optical type sensing device, they can only adopt the magnetic type sensing devices which cannot be affected by the environment condition, consequently, the corresponding precision is greatly reduced.
The present invention has arisen to mitigate and/or obviate the afore-described disadvantages.